OBJECTIVE: To investigate the efficacy of using intentionally cryopreserved epididymal sperm in selected cases of obstructive azoospermia. DESIGN: A retrospective, nonrandomized study. SETTING: Academic research environment. PATIENTS: One hundred forty-one couples undergoing first-time IVF/ICSI using either fresh or cryopreserved epididymal sperm. INTERVENTIONS: The epididymides were microsurgically aspirated. MAIN OUTCOME MEASURES: Clinical pregnancy rates. RESULTS: Motile sperm were obtained from all men. For the fresh group, the mean total sperm aspirated was 99 x 10(6) with 5.5 vials frozen per patient after ICSI and 82 x 10(6) with 4.7 vials frozen per patient in the cryopreserved group. No statistically significant difference in oocyte fertilization rate or number of embryos transferred was noted between groups. Of 108 patients using freshly aspirated sperm, 72 (66.7%) achieved clinical pregnancy. Of 33 patients in the group using cryopreserved sperm, 20 (60.6%) achieved clinical pregnancy (P=0.47). CONCLUSIONS: In selected ideal cases of unreconstructable azoospermia, elective open microsurgical epididymal sperm aspiration with cryopreservation yields pregnancy rates similar to that employing fresh sperm. The advantages of this method are: (1) Use of cryopreserved sperm obviates the logistics problems associated with the use of fresh sperm. (2) Abundant high-quality sperm can be cryopreserved in a single procedure for all future attempts at IVF/ICSI. Rarely, viable sperm will not be present after thawing, and fresh retrieval will be necessary.